At least four dead in California shooting

A gunman has killed three people in California, including at least one execution-style, in a series of shootings and carjackings before taking his own life.

Police say at least two other people were injured as the gunman fired randomly on other vehicles on a freeway, before he shot and killed himself near the city of Orange, south of Los Angeles.

The suspect was identified as 20-year-old Ali Syed, who was unemployed, had no criminal record, and was living at home with his parents and taking a class at a local college.

In all there were three murders and five attempted murders. The motive for the attacks was being investigated, said Orange County sheriff's spokesman Jim Amormino, in an afternoon update on the early morning shootings.

He described Syed as "kind of a loner (who) doesn't have a lot of friends".

The first killing was a woman found dead in the early hours in Syed's family home in Ladera Ranch. The woman was not known to his relatives, and police said they were working to identify her.

Syed then fled in an SUV, and "multiple incidents" occurred as he drove to nearby Tustin, about southeast of Los Angeles, said Tustin police department spokesman Paul Garaven.

In one of the first carjackings, Syed appeared "very polite" as he walked up to a gas station customer.